Switching converters are commonly used to provide electric power to many electronic devices. A transformer or an inductor is usually configured as a tank element in the switching converter. For example, an inductor is configured in a BUCK converter. A main switch is electrically coupled to the inductor. The main switch is turned ON and OFF so as to alternately store energy in the inductor and transfer the stored energy to the load.
Switching converter with peak current control has simpler system dynamics because it makes use of the available current sense information during normal operation. The main disadvantage of peak current control scheme is its susceptibility to noise in a current sense signal indicative of a current flowing through the inductor of the switching converter and to noise in the reference signal compared with the current sense signal. Thus the sub-harmonic oscillation will arise, and the switching converter with peak current control is unstable whenever the steady-state duty cycle is greater than 50%. To avoid this stability problem, the control scheme is usually modified by addition of an artificial ramp to the current sense signal.
FIG. 1 shows the waveforms of a prior art switching converter with peak current control, wherein Vs represents the current sense signal indicative of the current flowing through the inductor, Ipeak represents a current limit signal and Vsp represents the difference between the current limit signal Ipeak and the artificial ramp. As can be seen from FIG. 1, when the current sense signal Vs hits waveform Vsp, an over current condition is detected. Then the main switch is turned OFF and the current sense signal Vs decreases. Because of the existence of the artificial ramp, the actual current limit value is equal to the difference of the current limit signal Ipeak and the artificial ramp.
The present invention pertains to provide a switching converter with adaptive OFF time control which has precise current control.